It is known to provide a valve timing control apparatus that controls opening timing and closing timing of intake valves or exhaust valves, which are driven by a driven-side shaft of an internal combustion engine, by changing a rotational phase between a driving-side shaft and the driven-side shaft of the engine. For example, the valve timing control apparatus of JP2005-351182A changes the opening timing and closing timing of the valves through rotation of a vane rotor relative to a housing by changing a pressure of hydraulic oil in advancing chambers and a pressure of hydraulic oil in retarding chambers in the housing. The vane rotor of JP2005-351182A is made only of a plurality of metal plates, which are stacked one after another in the axial direction.
A size of the metal plate varies among the metal plates of the vane rotor. Therefore, the axial size and the radial size of the vane rotor vary from product to product. Particularly, the axial size of the vane rotor largely varies from product to product because of accumulation of size errors of the metal plates, which are stacked one after another in the axial direction. Therefore, a gap between the vane rotor and the housing cannot be reduced beyond a certain limit, and thereby oil leakage from the gap may possibly occur.
JPH11-81928A teaches another type of valve timing control apparatus, which changes opening timing and closing timing of the valves through rotation of a vane rotor relative to a housing by changing a pressure of hydraulic oil in advancing chambers and a pressure of hydraulic oil in retarding chambers in the housing.
In the valve timing control apparatus of JPH11-81928A, a seal member is installed to a radially outer end of each of vanes of the vane rotor. In a state where the pressure of the advancing chamber is larger than the pressure of the retarding chamber, the seal member is urged against a retarding chamber side wall surface of a corresponding groove of the vane rotor and an inner wall of the housing by a pressure of the hydraulic oil, which enters from the advancing chamber into a clearance between the seal member and the vane. In another state where the pressure of the retarding chamber is larger than the pressure of the advancing chamber, the seal member is urged against an advancing chamber side wall surface of the corresponding groove of the vane rotor and the inner wall of the housing by a pressure of the hydraulic oil, which enters from the retarding chamber into a clearance between the seal member and the vane.
In the valve timing control apparatus of JPH11-81928A, when the pressure difference between the advancing chamber and the retarding chamber is reduced, the differential pressure, which is a pressure difference between the pressure of the hydraulic oil in the advancing chamber and the pressure of the hydraulic oil in the retarding chamber and is applied to the seal member, is reduced. Therefore, the position of the seal member becomes unstable, and thereby the oil leakage may easily occur.
Furthermore, the hydraulic oil, which is pumped from an oil pump, is supplied to the clearance between the seal member and the vane of the vane rotor through the advancing chamber or the retarding chamber. Therefore, the pressure loss, which occurs in the path from the oil pump to the clearance, is relatively large. Thus, it is not possible to obtain a sufficient pressing force to press the seal member. As a result, the oil leakage can easily occur.